On Wed, 18 May 2005 12:15:05 +0100, "Bob Mannix"
wrote:

Bear in mind that 100mm dia pipe will create much more back pressure
than 150mm pipe!

You should worry! My toilet extractor fan (Xpelair) vents through a 75mm
pipe that runs through the flat roof to the fascia about 3-4m. You can't buy
extractor fans with smaller than 100mm outlets now (not that I can see). I
can't shove a bigger pipe through as it's full of insulation. Meanwhile the
fan bearing gets noisier and noisier ( Any suggestions, likewise,
welcome!

Can you take out some insulation and then run a 100mm pipe through?
If you can't do this you could look at reducing the speed of the fan
or buying a stronger fan!

My kitchen extraction also runs parallel in 75mm pipe for about 2m. I had to
convert right down to that - it still extracts enough but much slower than
it would with a bigger pipe, and much noisier. The flow is also non-linear
with fan speed, there's no point running it other than at the first position
as the noise goes up exponentially and the extraction just a bit!

I found it worthwhile to replace the pipework in my kitchen with
larger diameter round pipe. It made a big difference.

Mark